A variety of gravity separators have been developed for use in concentrating/separating various minerals and particles based on their relative specific gravity. Differences in the specific gravities of the different materials making up the feed mixture are used to achieve the separation of high specific gravity materials from the low specific gravity materials. Gravity separators include, but are not limited to, launders, riffles, hydroseparators, thickeners, clarifiers, elutriators, jigs, Eirich cones, spiral separators, hydrocyclones, hydrosizers, and settling cones. Although the primary criteria used to select a specific type of separator is the size and the physical nature of the materials to be separated, other factors may enter into the selection process including the desired rate of separation, the total quantity of material to be separated (i.e., short term versus long term needs), the size of the facility in which the separator is to be used, and the cost. The separations are conducted in a fluid, such as water or air, that acts both as a separation medium and as a transport medium.
Many different approaches have been taken to improving the concentration/separation efficiency and/or general operation of gravity separators. For example, U.S. Pat. No. 4,384,650 discloses a modification to a simple spiral separator that is designed for use with materials that do not vary greatly in specific gravity. The disclosed separator is similar to a conventional spiral separator in that it is comprised of a plurality of helical troughs or spirals mounted to an upright column. Unlike a conventional separator in which the separator trough is relatively uniform along its entire length, the trough of the disclosed separator includes a channel along the outer portion of the trough. The channel is narrow and deep near the top of the separator, becoming progressively wider in order to maintain pulp flow and avoid coarse and/or less dense particles from becoming stationary or stranded.
Another method of enhancing the performance of a separator is to combine conventional gravity separation with magnetic separation. For example, U.S. Pat. No. 4,565,624 and related U.S. Pat. No. 4,659,457 disclose retrofitting a conventional gravity separator with magnets. The disclosed systems use magnets mounted beneath the separation surface (e.g., trough or sluice, etc.) to enhance the separation of magnetic or weakly magnetic minerals from feed materials. In order to prevent build-up of magnetic or weakly magnetic particles on the flow surface, the magnetic field is varied over time. Disclosed techniques of varying the magnetic field include the use of electromagnets and altering the positions of permanent magnets relative to the flow surface.
U.S. Pat. No. 5,193,687 discloses a gravity-magnetic separation system in which permanent magnets are retrofitted under a metal separation trough such as the spiral cast-iron trough utilized in a conventional Humphreys spiral type gravity separator. The permanent magnets of the disclosed system are intended to be sufficiently strong to overcome the shielding effect of the trough structure while being weak enough to prevent excessive build-up of the magnetic material on the separation surface. In one embodiment of the system, the permanent magnets are comprised of neodymium, boron, and iron. In another embodiment, the magnets are comprised of cobalt and samarium. The patent also discloses the use of electromagnets of suitable strength.
U.S. Pat. No. 5,205,414 discloses a process for improving the recovery of non-magnetic heavy minerals in a gravity-magnetic separator. Specifically, the disclosed process adds magnetic material, for example ilmenite, magnetite, or iron filings, to the feed material of a gravity-magnetic separator. In one embodiment, the system is used in the processing of iron ore to recover magnetite as well as hematite. In another embodiment, the system is used in the treatment of heavy mineral sand ore containing rutile, zircon, and ilmenite.